Finer pattern formation using general photolithography techniques involves modifying exposure apparatuses. Particularly, the formation of a pattern with a pitch size of 60 nm or smaller by photolithography techniques requires special apparatuses, such as immersion photolithography developed in recent years, and requires enormous investments.
Therefore, various techniques have been studied for obtaining a fine pattern without using such expensive apparatuses. Among them, the most practical method includes forming a coating layer on an already formed resist pattern using a composition containing a water-soluble resin and, optionally, an additive, and thereby making the resist pattern finer. This technique allows, irrespective of exposure wavelengths, the formation of a fine pattern that exceeds the limits of photolithography. Such a technique has a short history and has merely been practiced for approximately 10 years. For example, the following methods have been proposed:    (1) a method including: forming a resist pattern; then applying thereonto a resist for forming mixing; forming a mixing layer by baking; and forming a pattern with a fine pattern size by developing (Japanese Patent Laid-Open No. 5-166717);    (2) a method for forming a fine pattern of an aqueous coat, including: forming a positive photoresist pattern on a substrate; subsequently uniformly exposing the pattern to electromagnetic radiation; then evenly applying thereonto an aqueous coat, and including: dissolving and removing (lifting off) the positive photoresist with an alkaline aqueous solution (Japanese Patent Laid-Open No. 7-191214);    (3) a method for achieving reduction in hole diameter or pitch width of a resist pattern, including: covering a resist pattern containing a material that generates an acid through exposure, with a resist containing a material that crosslinks in the presence of an acid; generating an acid in the resist pattern by heating or exposure; forming, as a coating layer of the resist pattern, a crosslinked layer in the interface to thicken the resist pattern (Japanese Patent Laid-Open No. 10-73927);    (4) a method for forming a fine pattern, including: preparing a fine pattern forming material by dissolving a completely water-soluble crosslinking agent and a water-soluble resin in an aqueous medium, the completely water-soluble crosslinking agent being selected from glycol lauryl having at least one imino group with a hydroxyalkyl group substituted for a hydrogen atom; and forming a resist pattern on a substrate using a chemically amplified resist containing an acid-producing agent; then providing thereon a coating film of the fine pattern forming material; forming a water-insoluble reaction layer in the interface between the resist pattern and the coating film by heat treatment; and subsequently removing an unreacted portion of the coating film with an aqueous solvent (Japanese Patent Laid-Open No. 10-73927);    (5) a method including: swelling a surface layer of a resist pattern by permeating thereinto a chemical solution containing a crosslinking agent and a swelling promoter, the crosslinking agent bringing about crosslinking in the presence of an acid; and forming a crosslinked film in the swollen surface layer of the resist pattern to form a second resist pattern (Japanese Patent Laid-Open No. 2001-100428);    (6) a method including: covering a resist pattern with a first upper layer containing an acid component; further forming thereon a second upper layer containing a basic component; then diffusing the acid component and the basic component into the first resist pattern and into the first upper layer, respectively, by heat treatment to form a solubilized layer in the resist pattern, while neutralizing the acid component with the basic component in proximity to the interface between the first and second upper layers; and removing the solubilized layer to reduce the width of the trace (Japanese Patent Laid-Open No. 2001-100428);    (7) a method for forming a finer resist pattern, including: applying a coat forming agent for a forming finer resist pattern onto a whole or partial surface of a resist pattern formed on a substrate, the coat forming agent containing a copolymer of a (meth)acrylic acid monomer and a water-soluble vinyl monomer; and heat-shrinking the resist pattern by additional heating (Japanese Patent Laid-Open No. 2003-84459); and    (8) a method for forming a resist pattern, including: applying a surfactant-containing solution onto a resist pattern; and then applying thereonto a resist pattern-thickening material containing a resin and a surfactant (Japanese Patent Laid-Open No. 2004-191465).
Furthermore, a finer resist pattern forming composition named AZ RELACS (registered trademark) is sold by AZ Electronic Materials.
These methods, in general, can easily form a fine pattern that exceeds the limits of photolithographic resolution. However, ultrafine pattern formation with a pattern size of 50 nm or smaller tends to cause defects and the like. Therefore, these methods still had room for improvement. Particularly, as a current trend, a film thickness is reduced for enhancing resist sensitivity. However, in this case, the minimum film thickness of a base substrate was sometimes insufficient for etching.    [Patent Literature 1] Japanese Patent Laid-Open Publication No. 166717/1993    [Patent Literature 2] Japanese Patent Laid-Open Publication No. 191214/1995    [Patent Literature 3] Japanese Patent Laid-Open Publication No. 73927/1998    [Patent Literature 4] Japanese Patent Laid-Open Publication No. 2000-267268    [Patent Literature 5] Japanese Patent Laid-Open Publication No. 2001-100428    [Patent Literature 6] Japanese Patent Laid-Open Publication No. 2002-6512    [Patent Literature 7] Japanese Patent Laid-Open Publication No. 2003-84459    [Patent Literature 8] Japanese Patent Laid-Open Publication No. 2004-191465